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Full text of "Circuits"

Cheap, Friendly, and Precise PCB Etching 



Make] Projects 



Cheap, Friendly, and Precise 
PCB Etching 

Written By: Quinn Dunki 



TOOLS: 


PARTS: 


Dremel (1) 


Pre-sensitized PCB (1) 


Tiny drill bits (1) 


Overhead transparency (1) 




Positive developer (1) 




Vinegar (1) 




Saltm 




Hvdroaen Peroxide (3%) (1) 




Nail polish remover (1) 



SUMMARY 

You can't throw a rock without hitting a tutorial on etching your own PCBs. They're 
everywhere, and there seem to be as many techniques as there are hackers. So why am I 
bothering to write another one? Well, there wasn't any single procedure that met all my 
goals, so I decided to synthesize a process from everyone else's ideas. This is what I came 
up with. 



For more details and better pictures, check out this site . 
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Pagel of 10 



Cheap, Friendly, and Precise PCB Etching 



Step 1 — Cheap, Friendly, and Precise PCB Etching 




• My goals for the process are 
fourfold: 

• Cheap. Whatever I do needs to 
cost as little as possible. 

• Clean. I want to minimize nasty 
chemicals that are difficult to 
use, store, and dispose of. 

• Tidy. I don't want to invest in 
bulky equipment like laminators 
or laser printers. 

• Precise. I want to be able to use 
small traces, and make compact 
boards. 

# Here's a sample of the finished 
product. Those are 0.01" traces, 
and they all worked on the first try. 
This technique is great for small 
boards and complex layouts. 
Excuse the mess on the three large 
pads at the bottom. More on that 
later. 



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Cheap, Friendly, and Precise PCB Etching 



Step 2 




• The first step is to make a board 
layout. You can't do much better 
than Eagle, although the learning 
curve can be a bit steep. The 
SparkFun tutorials are a really 
good place to start. After that, read 
the manuals that come with the 
software. 

• Here's my board, in Eagle. Note 
that I tell the autorouter to use 
0.01" traces on a 0.05" grid, which 
is contrary to what many tutorials 
for hobbyists say. This etching 
technique works well on traces that 
small, and you can make a much 
more complex board without 
resorting to dual layers or lots of 
jumpers. A layout grid that is 
double the resolution of the 
component grid solves a lot of 
routing problems, in my 
experience. 



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Cheap, Friendly, and Precise PCB Etching 



Step 3 




• I hide all layers in Eagle except the 
bottom traces, then print it to a 
PDF. This works great because it's 
very high pixel density. That's 
critical to getting small traces to 
work. Many tutorials will tell you to 
use the Image Export operation, 
but that generates pixelated images 
that mess up small traces. 

• Next, I bring that PDF to FedEx 
Office (formerly Kinko's), and print 
it on regular paper. I then 
photocopy it to overhead 
transparency. Kinko's self-serve 
printers will not let you print to 
acetate, but they will let you 
photocopy onto it. The self-serve 
printers are a tenth of the cost of 
going up to the counter, so this 
two-step method is well worth it. 

• Why not print it at home? Printers 
are bulky, ink is ridiculously 
overpriced, and Kinko's self-serve 
is 10 cents a sheet. That's a lot of 
PCBs for the cost of owning a 
printer. 

• If any part of the printout isn't 
totally opaque, use a Sharpie to 
cover it up. I got a bit sloppy with 
mine while touching up the three 
large pads. You can see the result 
of that in the final product. 



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Cheap, Friendly, and Precise PCB Etching 



Step 4 




• Next, I use the photoresist method 
to transfer the pattern to the board. 

• This video tutorial from Jameco 
explains it far better than I could. 
Plus, Collin Cunningham is 
hilarious. You only need to watch 
up to the 4:10 mark. After that, his 
process is different than what I'm 
describing. 

• You'll need Positive Developer, as 
well. This is the one and only 
unpleasant chemical involved. As 
much as I like Jameco, this stuff 
from Mouser is 10 times cheaper 
and works just as well: 

• As shown in the video above, I 
apply the acetate to a presensitized 
PCB. These are almost as cheap 
as regular copper boards, and 
extremely easy to work with. You 
can expose them with a regular 
lamp and an old picture frame. It 
takes only minutes, and because 
it's a photographic process, it's 
exceptionally precise. Far more so 
than the song & dance people do 
with laser printer toner, magazine 
paper, a clothes iron, and water 
soaking. I expose the board for 
twenty minutes with the lamp about 
as close as I can get it. 



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Cheap, Friendly, and Precise PCB Etching 



Step 5 



s. 












• -: 




_3b 





• Once the board is exposed, 
sloshing it in a solution of 10 parts 
warm water and 1 part developer 
reveals the pattern in all its glory. 
This takes under a minute. 



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Cheap, Friendly, and Precise PCB Etching 
Step 6 



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Cheap, Friendly 



ise PCB Etching 




• Now we're ready for the real work - 
the etching. For this portion, I can't 
give enough thanks to Stephen 
Hobley and his etching process, 
laid out in this video . 

• For more details on this process, 
and how it works, check out his 
site . 

• Yes, you can etch a PCB with 
nothing more than hydrogen 
peroxide, vinegar, and salt! This 
mix is so benign you could almost 
eat it. Please do not eat it. If you do 
eat it, please do not tell the judge I 
told you to eat it. Your Honor, if 
you're reading this, I explicitly told 
people not to eat it. 

• This photo shows my board etching 
happily in Stephen Hobley's 
mixture of 1 part peroxide to 1 part 
vinegar (which we didn't eat, 
right?). 

• As Stephen explains, dump some 
salt in there to start, and as needed 
to keep the bubbles going. Also, 
open a window, because it smells a 
bit funky. If this nearly-edible PCB 
mixing method seems too good to 
be true, well, there is a catch. It's 
slow. The board will require about 
an hour of soaking, with occasional 
sloshing and adding salt. Sure, the 
ferric chloride or muriatic acid 
methods are faster, but those 
chemicals are nasty and 



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Cheap, Friendly, and Precise PCB Etching 



expensive. 
• With this method, you can etch a 
PCB on your kitchen counter, with 
stuff you probably already have in 
your cupboard. As slow as this is, 
it's sure faster and cheaper than 
sending away to a PCB house. 



Step 7 




• Isn't it purrrty? To drill the normal 
component lead holes, I use a #69 
(.0292" or 0.75mm) bit in a Dremel. 
Use larger bits as needed for 
switch terminals, etc. In my 
experience, you really don't need a 
drill press like everyone says. Just 
hold the board by the edge with one 
hand (wear gloves), and drill with 
the Dremel in the other hand. Wear 
eye protection and a paper mask! 
Fiberglass dust is nasty. 

• Yes, I forgot to add a couple of 
vias, so there are two under-board 
jumpers. Oh well, live and learn. So 
what is this device, you might ask? 
Well, that's a story for another 
time... 

• For more details and better 
pictures, be sure to check out this 
site . 



For more details and better pictures, check out this site . 

© Make Projects www.makeprojects.com 



Page 9 of 10 



Cheap, Friendly, and Precise PCB Etching 

This document was last generated on 2012-11-01 09:06:48 PM. 



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